1. Field of the Disclosure
The present disclosure relates to a variable resistance non-volatile memory device including a variable resistance element which reversibly changes its resistance value by application of electric pulses, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, with progresses of digital technologies, electronic devices such as portable information devices and information home electric appliances have been developed to provide higher functionalities. With achievement of the higher functionalities of these electronic devices, semiconductor elements incorporated into these electronic devices are developed to provide further miniaturization and a higher speed. Among them, as a non-volatile device in next generation which has a potential of replacing a flash memory, a resistive random access memory (ReRAM) including the variable resistance element has been studied and developed.
The variable resistance element refers to an element having a characteristic in which it reversibly changes its resistance state (resistance value) in response to an electric signal, and retains the changed resistance state. By allocating information to resistance states of the variable resistance element, the information can be stored in a non-volatile manner. Specifically, for example, by allocating “0” to one of a low-resistance state corresponding to a relatively smaller resistance value and a high-resistance state corresponding to a resistance value which is greater than that corresponding to the low-resistance state, and “1” to the other, binary information can be stored.
The variable resistance element includes, for example, a first electrode, a second electrode, and a variable resistance layer which is disposed between the first electrode and the second electrode and includes two metal oxide layers which are different in degree of oxygen deficiency and are stacked together. By applying an electric pulse (e.g., voltage pulse) between the first electrode and the second electrode of the variable resistance element, the resistance state of the variable resistance layer is changed from the high-resistance state to the low-resistance state or from the low-resistance state to the high-resistance state. In this variable resistance memory, it is desired that the low-resistance state and the high-resistance state corresponding to the binary information can be clearly distinguished from each other, and switching between the low-resistance state and the high-resistance state can take place stably and at a high speed.
Under the circumstances in which there are such demands, a configuration for attaining high-speed and stable switching between the low-resistance state and the high-resistance state, by suppressing non-uniformity of resistance values of variable resistance elements, has been proposed (see International Publication No. 2012/001978).
International Publication No. 2012/001978 discloses that a stacked-layer structure including a first electrode layer, a variable resistance material layer and a second electrode layer is formed, then a hard mask is formed using a photoresist mask having a shape (dot shape) in which corner portions in a planar shape are receded toward a center portion, and then the stacked-layer structure is etched using the hard mask, thereby forming the variable resistance element. The variable resistance element fabricated in this method is allowed to have round portions without corner portions having an angle of 90 degrees (variable resistance elements of dot shape are formed). According to International Publication No. 2012/001978, this method is said to be able to lessen non-uniformity of etched amounts of variable resistance material layers.